The study, published in Acta Neuropathologica, showed a practically complete recovery occurred in 50 percent of the animals after eight days of treatment of the drug normally used in the treatment of erectile dysfunction.

Drs. Agustina Garci and Juan Hidalgo of the Universitat Autonoma de Barcelona studied the effects of a treatment using sildenafil -- sold under the brand name Viagra -- in an animal model of multiple sclerosis.

If given shortly after disease onset, the scientists say they observed the drug reduced the infiltration of inflammatory cells into the white matter of the spinal cord, reducing damage to the nerve cell's axon and facilitating myelin repair.

Multiple sclerosis is caused by the loss of myelin sheaths around the axons -- a long, slender projection of a nerve cell that conducts electrical impulses away from the neuron's cell body -- affecting the ability of neurons to communicate and neurodegeneration in different areas of the central nervous system. There is currently no cure for the disease, but some drugs help fighting symptoms, the researchers say.

I don't know, but I guess I would not be very optimistic that Viagra would help with most cases of ME/CFS, because of the low total blood volume frequently found in this disorder. Dilating the blood vessels will likely make it more difficult to get enough blood flow to the brain, especially when upright.